[tip/urgent] Avoid deadlock in rt_mutex_start_proxy_lock()

[tip/urgent] Avoid deadlock in rt_mutex_start_proxy_lock()

[Darren Hart]

From: Darren Hart <dvhltc@us.ibm.com>

In the event of a lock steal or owner died, rt_mutex_start_proxy_lock() will
give the rt_mutex to the waiting task, but it fails to release the wait_lock.
This leads to subsequent deadlocks when other tasks try to acquire the
rt_mutex.

I also removed a few extra blank lines that really spaced this routine out.
I must have been high on the \n when I wrote this originally...

Note: This is the mainline version, a separate patch was sent for [RT]

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>
CC: Dinakar Guniguntala <dino@in.ibm.com>
CC: John Stultz <johnstul@us.ibm.com>
---

 kernel/rtmutex.c |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)


diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index fec77e7..0f2b9bb 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -1039,16 +1039,14 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 	if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
 		/* We got the lock for task. */
 		debug_rt_mutex_lock(lock);
-
 		rt_mutex_set_owner(lock, task, 0);
-
+		spin_unlock(&lock->wait_lock);
 		rt_mutex_deadlock_account_lock(lock, task);
 		return 1;
 	}
 
 	ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
 
-
 	if (ret && !waiter->task) {
 		/*
 		 * Reset the return value. We might have
-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team

[tip:core/urgent] rtmutex: Avoid deadlock in rt_mutex_start_proxy_lock()

[tip-bot for Darren Hart]

Commit-ID:  1bbf20835c4e088667a090ce6523a0f70b62dc76
Gitweb:     http://git.kernel.org/tip/1bbf20835c4e088667a090ce6523a0f70b62dc76
Author:     Darren Hart <dvhltc@us.ibm.com>
AuthorDate: Wed, 5 Aug 2009 12:05:21 -0700
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 6 Aug 2009 05:50:21 +0200

rtmutex: Avoid deadlock in rt_mutex_start_proxy_lock()

In the event of a lock steal or owner died,
rt_mutex_start_proxy_lock() will give the rt_mutex to the
waiting task, but it fails to release the wait_lock. This leads
to subsequent deadlocks when other tasks try to acquire the
rt_mutex.

I also removed a few extra blank lines that really spaced this
routine out. I must have been high on the \n when I wrote this
originally...

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Dinakar Guniguntala <dino@in.ibm.com>
Cc: John Stultz <johnstul@linux.vnet.ibm.com>
LKML-Reference: <4A79D7F1.4000405@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 kernel/rtmutex.c |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index fcd107a..29bd4ba 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -1039,16 +1039,14 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 	if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
 		/* We got the lock for task. */
 		debug_rt_mutex_lock(lock);
-
 		rt_mutex_set_owner(lock, task, 0);
-
+		spin_unlock(&lock->wait_lock);
 		rt_mutex_deadlock_account_lock(lock, task);
 		return 1;
 	}
 
 	ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
 
-
 	if (ret && !waiter->task) {
 		/*
 		 * Reset the return value. We might have